The present invention relates to a fan apparatus including a fan revolved to produce a flow of air, and more particularly to a fan apparatus capable of reducing noise generated due to the revolution of the fan, and a shroud for use with the fan apparatus.
Heretofore, a side-branch type pulsation reducing apparatus disclosed in JP, A, 9-425756, for example, has been known as a prior-art apparatus in which a small stream path branched from a main stream of a fluid induced by a fluid machine, and a stream going through the branched stream path and back is caused to interfere with the main stream, thereby properly modifying the form of a wave propagating in the main stream.
The disclosed apparatus is installed in, e.g., a construction machine such as a hydraulic excavator. A bottom-equipped side branch is branched from and connected to a delivery line of a hydraulic pump driven by an engine. The pulsation of a hydraulic fluid delivered from the hydraulic pump propagates through the delivery line and a passage in the side branch as well. The pulsation of the hydraulic fluid propagating through the side branch passage is reflected by a wall surface at the end of the side branch, and returns to the delivery line again through the side branch passage. By previously deciding a particular frequency of the pulsation wave to be reduced and appropriately adjusting a length of the side branch passage depending on the particular frequency, therefore, the pulsation wave of the hydraulic fluid, which goes through the side branch passage and returns to the delivery line, is caused to interfere with the pulsation wave propagating straightforward through the deliver line in such a relationship that the hills of one wave collide with the valleys of the other wave. Of the pulsation of the hydraulic fluid advancing straightforward through the deliver line, the pulsation of the particular frequency can be thereby reduced primarily. In this case, the particular frequency is set to, e.g., a pump pulsation frequency (150-1000 hertz) that corresponds to the engine revolution speed of a hydraulic excavator during ordinary excavating work.
On the other hand, an engine apparatus installed in a construction machine and a motor vehicle, for example, comprises an engine, a rotary shaft to which a driving force of a crankshaft of the engine is transmitted, a fan fitted over the rotary shaft, a heat exchanger disposed in front (upstream) of the fan, and a shroud fixed downstream of the heat exchanger. An propeller fan is usually employed as the fan in many cases, and the heat exchanger includes a radiator to which engine cooling water is supplied in a circulating manner. When the engine is driven, rotation of the crankshaft is transmitted to the rotary shaft to revolve the fan, whereupon air is introduced to the heat exchanger from the upstream side for cooling the heat exchanger. The air having passed the heat exchanger is introduced to the suction side of the fan through the shroud and flows into the fan. Then, the air flowing out of the fan further cools the engine.
It has been hitherto known that noise occurs in the above engine apparatus due to revolution of the fan. One conceivable method of reducing the noise is to apply the structure of the above apparatus disclosed in JP, A, 9-42576 to the fan in the engine apparatus. Specifically, by providing a side branch which has a predetermined length and is branched from a wall surface of the shroud defining an air flow passage in an enclosed space extending from the heat exchanger to the fan, a sound wave going through a side branch passage and returning to the shroud is caused to interfere with a sound wave propagating straightforward downstream in the shroud. Of the noise propagating in the shroud, the noise component of a particular frequency can be thereby reduced primarily. In this case, the particular frequency is set to, e.g., a frequency of the fan rotary shaft that corresponds to the engine revolution speed of a hydraulic excavator during ordinary excavating work.
However, the inventors of this application have found that the noise cannot be reduced sufficiently by applying the structure of the above apparatus disclosed in JP, A, 9-42576 to the fan in the engine apparatus. The reasons are as follows.
In the structure introducing air to the suction side of the fan through the shroud like the above engine apparatus, there are two main noise sources. The first is wind chopping noise generated from the ends of fan blades upon the blades revolving while chopping the air flow (referred to simply as wind chopping noise hereinafter). The wind chopping noise occurs regardless of whether the shroud is provided or not. The second is collision noise generated from the wall surface of the shroud upon an air flow colliding against the shroud wall surface after coming out of the fan (referred to simply as collision noise hereinafter). Of those noise sources, the collision noise is dominant in the structure introducing air to the suction side of the fan through the shroud. The side branch type structure such as employed in the apparatus of JP, A, 9-42576 intends to reduce the wind chopping noise primarily, and therefore cannot reduce the collision noise. Thus the noise cannot be reduced sufficiently as a whole.
In consideration of the above result, the inventors of this application have found that it is effective to damp a radial component of the air flow coming out of the fan for reducing the collision noise.
An object of the present invention is to provide a fan apparatus capable of sufficiently reducing noise generated due to revolution of a fan, and a shroud for use with the fan apparatus.
To achieve the above object, the present invention provides a fan apparatus comprising a fan having a plurality of blades and producing an air flow with revolution thereof, and at least one shroud disposed upstream of the fan and introducing the air flow to the suction side of the fan, wherein damping means for taking in the air flow coming out of the fan and damping a radial component of the air flow under an interference action is provided in an outer periphery side of the fan.
The air flow produced with the revolution of the fan is introduced to the suction side of the fan through the shroud, and flows out to the blown-off side of the fan. At this time, noise generates from two main noise sources, i.e., wind chopping noise generated from the ends of fan blades upon the blades turning while chopping the air flow with the revolution of the fan, and collision noise generated from a wall surface of the shroud upon the air flow colliding against the shroud wall surface after coming out of the fan. Of those noise sources, the latter is dominant. Usually, a downstream portion of the shroud is arranged in overlapping relation to the radial outer periphery side of the fan to some extent, and the air flow coming out of the fan radially outward collides against the downstream portion of the shroud, thereby generating the collision noise.
Taking into account the above, in the present invention, the damping means is provided in the outer periphery side of the fan to take in the air flow coming out of the fan and to damp the radial component of the air flow under an interference action, whereby the collision of the air flow against the shroud wall surface is moderated. It is therefore possible to reduce the collision noise that is the dominant noise source, and to reduce the noise generated due to the revolution of the fan sufficiently.
In the above fan apparatus, preferably, the damping means includes at least one bottom-closed pipe disposed with the open side thereof facing the outer periphery side of the fan.
Also, to achieve the above object, the present invention provides a fan apparatus comprising a fan having a plurality of blades and producing an air flow with revolution thereof, and at least one shroud disposed upstream of the fan and introducing the air flow to the suction side of the fan, wherein the fan apparatus includes at least one bottom-closed pipe disposed with the open side thereof facing an outer periphery side of the fan, the bottom-closed pipe having an axial length L that satisfies a relationship of L=mxc3x97(xcfx80xc3x97R)/N [m] where R is the distance [m] from an outer periphery of the blade to an axis of the fan, the number of the blades is N [pieces], and m is an integer not less than 1.
Assuming that the distance from the outer periphery of the blade to the axis of the fan is R [m], a radial component Va [m/sec] of the air flow flowing out at a speed V [m/sec] to the blown-off side of the fan is nearly equal to a circumferential speed at a tip end of the blade of the fan, and therefore is expressed by;                               V          a                =                  R          ⁢                      xe2x80x83                    ⁢          ω                                        =                  R          ⁡                      (                          2              ⁢                              π                /                T                                      )                              
where xcfx89 is the angular speed [rad/sec] and T is the cycle [sec] required for the fan to make one revolution.
Also, assuming that a period of time lapsed from the time at which one blade passes a certain point to the time at which the next blade passes the same point is TN [sec] and the revolution speed of the fan is n [rpm], TN is expressed by:
TN=60/(nxc3x97N)
At this time, since the relationship of
T=Nxc3x97TN
exists between T and TN, the following is resulted:
T=60/n
By using the above equation, Va is expressed by:                               V          a                =                  2          ⁢          π          xc3x97          R          xc3x97                      (                          n              /              60                        )                                                  =                              (                          2              ⁢              π              xc3x97              R              xc3x97              n                        )                    /          60                    
Here, in the present invention, since the fan apparatus includes the bottom-closed pipe disposed with the open side thereof facing the outer periphery side of the fan, at least part of the radial component of the air flow flowing out to the blown-off side of the fan flows into the bottom-closed pipe. However, since the end of the bottom-closed pipe opposite to the open side is closed, the air flow having entered the pipe is turned by the closed end and returns to the open side again. Given the speed of the air flow flowing into the bottom-closed pipe being Va, the time TL [sec] required for the air flow to go through the pipe and return it expressed as follows on an assumption that the axial length of the bottom-closed pipe is L [m]:                               T          L                =                  2          ⁢                      L            /                          V              a                                                              =                  2          ⁢                      L            /                          {                                                (                                      2                    ⁢                    π                    xc3x97                    R                    xc3x97                    n                                    )                                /                60                            }                                                              =                  2          ⁢          L          xc3x97                      (                                          60                /                2                            ⁢              π              xc3x97              R              xc3x97              n                        )                                                  =                  60          ⁢                      L            /                          (                              π                xc3x97                R                xc3x97                n                            )                                          
Because the bottom-closed pipe is constructed so as to satisfy the relationship of L=mxc3x97(xcfx80xc3x97R)/N in the present invention, TL is expressed by:                               T          L                =                  60          ⁢                                    {                              m                xc3x97                                                      (                                          π                      xc3x97                      R                                        )                                    /                  N                                            }                        /                          (                              π                xc3x97                R                xc3x97                n                            )                                                              =                              (                          60              ⁢              π              xc3x97              m              xc3x97                              R                /                N                                      )                    /                      (                          π              xc3x97              R              xc3x97              n                        )                                                  =                  60          xc3x97                      m            /                          (                              n                xc3x97                N                            )                                          
Accordingly, the relationship of
TL=mxc3x97TN
is obtained. Stated otherwise, when the radial component of the air flow produced by one blade is turned by the closed end of the bottom-closed pipe and returns to the radially inward open side of the bottom-closed pipe, the next blade or any of the subsequent blades passes just the open side of the bottom-closed pipe. Therefore, the returned air flow collides with the new air flow produced by the next or other blade and advancing radially outward so as to cancel out each other. This phenomenon is repeated successively during the revolution of the fan, whereby the radial component of the air flow coming out of the fan can be damped.
In the above fan apparatus, preferably, the shroud is provided in number one, and the bottom-closed pipe is provided on a fan surrounding portion of the shroud.
In the above fan apparatus, preferably, the bottom-closed pipe is provided to project outward of the fan surrounding portion of the shroud.
In the above fan apparatus, preferably, the bottom-closed pipe is provided to extend along the inner side of the fan surrounding portion of the shroud.
In the above fan apparatus, preferably, the shroud is provided in number two and comprises a first shroud surrounding the fan and a second shroud provided upstream of the first shroud and introducing the air flow to the first shroud, and the bottom-closed pipe is provided on a fan surrounding portion of the first shroud.
Further, to achieve the above object, the present invention provides a shroud disposed upstream of a fan having a plurality of blades and producing an air flow with revolution thereof, the shroud introducing the air flow to the suction side of the fan, wherein a shroud includes damping means for taking in the air flow coming out of the fan and damping a radial component of the air flow under an interference action.